Conventionally, a combined heat exchanger configured to be capable of exchanging heat among three types of fluid is known. For example, in a heat exchanger disclosed in Patent Document 1, a combined heat exchanger is configured to be capable of exchanging heat between a refrigerant of a refrigeration cycle and outdoor air (outside air), and exchanging heat between coolant for cooling engine and the outside air.
Specifically, in the heat exchanger of Patent Document 1, refrigerant tubes in which the refrigerant flows and coolant tubes in which the coolant for an external heat source flows are arranged alternately in a stacked manner. Outer fins are arranged in outside air passages through which the outside air flows. Each of the outer fins is provided between the refrigerant tube and the coolant tube adjacent to each other and configured to allow heat transfer between the refrigerant tubes and the coolant tubes. Accordingly, not only the heat exchanges between the refrigerant and the blown air and between the coolant and blown air, but also the heat exchange between the refrigerant is the coolant can be achieved.
Therefore, for example, at the time of defrosting for removing frost attached to the refrigerant tubes, heat of the coolant can be transferred to the entire area of the refrigerant tube, so that the heat of the coolant can be effectively used.